Recently the mobile terminals such as a laptop computer, a cell phone, PDA or so has become extremely common, and as the power supply of these mobile terminals, a lithium ion secondary battery has been used in many cases. As the demanding characteristics of the mobile terminal power supply, the high capacity may be mentioned; however currently the capacity of the battery using the graphite type negative electrode is saturated, thus it is difficult to make large increase in the capacity. Thus, the use of silicon (Si) and tin (Sn) or the alloy thereof as the negative electrode active material is being thought in order to attain larger capacity (Patent document 1).
However, when the charge and discharge is carried out in such lithium ion secondary battery, the negative electrode active material expands and contracts during the insertion and extraction release of the lithium and causes a crack in the negative electrode layer. If, further charge-discharge are repeated under such condition, then the negative electrode layer can not withhold the rapid expansion and contraction of the negative electrode active material and due to the cracks in the negative electrode being spread or so, the negative electrode layer may be released and slip off.
Therefore, it is demanded to improve the cycle characteristics by solving such problems. Thus, in order to improve such cycle characteristics, the Patent document 2 describes the technology to manufacture hollow particles of alloy; however, such hollow particle of alloy did not necessary allow to obtain the sufficient cycle characteristics. Also, during the press of the electrode, the corruption of the hollow particle of alloy occurred, and it was not possible to control the desired density.
Said document also describes the method of removing the core portion made of polymer by heat treating after the production of the electrode. However, there are some problems such as lowering the conductivity or so since the current collector foil is oxidized.
Also, even when said core portion is left, there were still problems such that the sufficient charge-discharge cycle can not be obtained.